1. Technical Field
The present disclosure relates to a semiconductor light source driving apparatus that supplies a semiconductor light source with a drive current that has been subjected to a high-speed pulse width modulation.
2. Description of Related Art
Unexamined Japanese Patent Publication No. 2004-147435 discloses a circuit for driving LEDs (Light Emitting Diode) or other light emitting devices. This drive circuit outputs a constant pulse current by reducing influences of temperature fluctuations and an unstable source voltage, and variations in properties of the light emitting devices.
The above light emitting device drive circuit that drives LEDs, for example, includes a switch, error signal generating means, signal retaining means, and switching power supply control means. The switch intermittently supplies power from a switching power supply to a driven target. The error signal generating means generates error signals representative of errors between a target signal and detected signals output from detection means that detects a current flowing through the driven target and generates the detected signals in accordance with the detection results. When the switch is in the ON state, the signal retaining means averages the error signals generated by the error signal generating means. When the switch is switched from the ON state to the OFF state, the signal retaining means retains the averaged error signal. Then, when the switch is switched from the OFF state to the ON state, the signal retaining means sets the signal level of the retained error signal as an initial signal level and starts to average error signals again. In the switch-off state, the switching power supply control means stops the supply of power from the switching power supply to the driven target. In the switch-on state, the switching power supply control means supplies power from the switching power supply to the driven target while controlling the amount of the power in accordance with the averaged error signal obtained from the signal retaining means.
The above configuration can provide a drive circuit that outputs a constant pulse current by reducing influences of temperature fluctuations, an unstable source voltage, and variations in device properties.